Two groups of 4 monkeys (Macaca mulatta) were irradiated. The first group received 4 doses of 500 rads over 2 weeks. Considerable desquamation of the oral mucosa occurred. Rampant caries developed but was soon followed by osteonecrosis of the lower jaw. The second group was given 250 rads twice weekly for 2 weeks using Cobalt 60 as a radiation source. The flow of saliva rapidly diminished within 3 weeks of treatment. The animals were fed a diet rich in sugar. In a matter of weeks carries developed which clinically can not be distinguished from that which occurs in irradiated humans. Large numbers of Strep. mutans have been isolated from the irradiated animals. Plaque fluid is now being examined.